A conventional modern smart phone may include a system on chip (SOC), which has a processor and other operational circuits. Specifically, an SOC in a smart phone may include a processor chip within a package, where the package is mounted on a printed circuit board (PCB) internally to the phone. The phone includes an external housing and a display, such as a liquid crystal display (LCD). A human user when using the phone physically touches the external housing and the display.
As the SOC operates, it generates heat. In one example, the SOC within a smart phone may reach temperatures of 80° C.-100° C. Furthermore, conventional smart phones do not include fans to dissipate heat. During use, such as when a human user is watching a video on a smart phone, the SOC generates heat, and the heat is spread through the internal portions of the phone to the outside surface of the phone.
The outside surface of the phone is sometimes referred to as the “skin.” The outside surface includes the part of the external housing that is physically on the outside of the phone as well as any other externally-exposed portions, such as an LCD display. It is generally accepted that the skin of the phone should not reach temperatures higher than about 40° C.-45° C. due to safety and ergonomic reasons. As noted above, the SOC within the smart phone may reach temperatures of 80° C.-100° C., although the temperature of the SOC is not felt directly at the skin of the phone. Instead, heat dissipation within the phone often means that the skin temperature of the phone is at a lower temperature than the SOC temperature. Furthermore, whereas changes to SOC temperature may be relatively quick (e.g., seconds), changes to device skin temperature may be relatively slow (e.g., tens of seconds or minutes).
Conventional smart phones include algorithms to control the skin temperature by reducing a frequency of operation of the SOC when a temperature sensor in the SOC reaches a threshold level. However, SOC temperature can be a poor proxy for device skin temperature.